1. Field of the Invention
The present invention relates in general to sterilization water compatible products. In particular, the present invention relates to an improved method and apparatus for sterilizing particulate water compatible products at moderate pressures, typically food items, which includes an incremental pressure reduction that permits the final sterilized product to be packaged under normal atmospheric conditions.
2. Description of the Related Art
It has long been known to subject products to a sterilization process prior to packaging to prevent spoilage of the product, infection of end users with dangerous bacteria, etc. In particular, it has been known to subject particulate food products such as sliced vegetables, chopped meats, etc. to sterilization prior to packaging the particulate food product in containers, typically metallic cans.
For such water compatible products it has been common to perform the sterilization by passing the particulate product through a conduit having steam inlet openings along its length. As the steam is added to the particulate product, the temperature of the product is raised to a sterilization temperature sufficient to eliminate biological contamination of the product. The mix of product and steam is maintained under high pressure by conveyance pumps as the steam condenses to the liquid phase, thereby a great deal of heat is transferred to the product. The high temperature liquid and vapor permeates the product and provides sterilization.
It is only this increased pressure which maintains the steam in the liquid phase at the sterilization temperature. Were the pressure to be reduced, the liquid would flash to a vapor phase. As the high temperature liquid has permeated the product, this flashing from the liquid to the vapor phase would literally explode certain solid products if the heated and pressurized product were merely vented to atmospheric or an excessive reduced pressure. To avoid such explosive flashing, it has been known to dispense the product from the sterilizing conduit into a pressure tank having a sufficient pressure therein to prevent such flashing. This allows the product to be packaged within the pressure tank maintaining the required pressure on the system until the product has cooled sufficiently to eliminate the possibility of flashing at atmospheric pressure. While this arrangement is serviceable, the addition of the steam to the product raises the water content of the product mix, with such moisture rise being undesirable in many instances. Additionally, it requires human exposure during the packaging process, such that workers inside the tank are exposed to the high pressures necessary to prevent flashing.